1. Impression Evidence

2. Puzzle
Detective Logan surveys the scene. A woman is shot to death and is lying face down in the parking lot. A light snow covers the ground. Leading to the body is a set of footprints which run between two sets of parallel tracks. Leading away from the dead woman are just two sets of parallel tracks. What person should Detective Logan be looking for?

3. Bigfoot Buttocks Imprint Strongest Evidence Yet
By Kurt Kleiner

5. IMpression Evidence
Impression evidence physical evidence that results from the contact between two objects or surfaces
One of the largest classes of evidence
Falls into three types:
Imprint
Indentation
Striation

6. Imprint
Two dimensional product formed as one object transfers material onto a surface
- Can be patent (visible) or latent (invisible)

7. Latent Impressions
Impressions hidden to the eye but can be visualized through the use of special dusting and electrostatic techniques or chemical developers
Oils, fine soil, and other debris can be carried onto clean floors
Clean shoes or feet can transfer materials to a newly waxed or polished floor

8. Indentations
Three dimensional impressions which are left when one object comes in contact with the surface of a softer material, such as snow, mud, soil, or soap

9. Striations
 Occurs when an object comes in contact with a softer surface, creates an indentation, and then the object moves

10. Toolmark Identification
A tool mark is any impression, scratch, or abrasion made when contact occurs between a tool and an object
The impressions made by the tools could link the tool to a crime scene and ultimately to the tool’s owner

11. Collecting Impression Evidence
Can be broken into three different steps:
1. Photographing the impressions
2. Lifting latent impressions
3. Casting plastic impressions

12. Photographing Impression Evidence
Photographs should be taken before anyone alters or touches the impression
Impression should fill field of view
A picture of the impression by itself
An identifying label and a ruler in position should be placed in the second and subsequent pictures
Provides scale
Picture should be taken perpendicular to impression and at a couple different angles
If left on a dark surface, criminalist might do magnesium smoking – this leaves a white residue (magnesium oxide) on the surface allowing details to show up

13. Lifting Latent Impressions
Several different methods to make latent impressions visible:
Luminol – causes blood to glow in the dark
Footprints become visible and can be photographed
Dusting – like with fingerprints
Reveals impression and makes possible for photographs and lifting

14. Electrostatic Dusting
Works by applying a small electrostatic charge on a piece of lifting film, which is then placed over the latent print
The film picks up and holds the dust of the latent print
Can be used to lift impressions from paper, flooring, carpeting, pavement

15. Gel Lifting A gel lifter is a layer of thick gel
sandwiched between paper
backing and a plastic cover sheet
Best used on oily or moist impressions
Print is first dusted with powder
Protective cover is peeled off lifter and gel is pressed over the print
Gel lifter is removed and the cover is replaced
Gel lifter is photographed

16. Casting Plastic Impressions
A three dimensional impression is called a cast and may be made to preserve physical evidence
Methods vary depending on what materials casts are left in
Plaster of Paris – sand or dirt
Dental stone – snow
Hardens faster than Plaster of Paris
Silicone – typically used in tool marks